remove custom build apis from public api for now

Author: jakemac53

e2e_example/lib/copy_builder.dart

@@ -4,6 +4,8 @@
 import 'dart:async';
 
 import 'package:build/build.dart';
+import 'package:build/src/generate/input_set.dart';
+import 'package:build/src/generate/phase.dart';
 
 // Makes copies of things!
 class CopyBuilder extends Builder {

e2e_example/tool/build.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 import 'package:build/build.dart';
+import 'package:build/src/generate/build.dart';
+import 'package:build/src/generate/build_result.dart';
 
 import 'package:e2e_example/copy_builder.dart';
 

lib/build.dart

@@ -9,9 +9,5 @@ export 'src/asset/writer.dart';
 export 'src/builder/build_step.dart';
 export 'src/builder/builder.dart';
 export 'src/builder/exceptions.dart';
-export 'src/generate/build_result.dart';
-export 'src/generate/build.dart';
-export 'src/generate/input_set.dart';
-export 'src/generate/phase.dart';
 export 'src/package_graph/package_graph.dart';
 export 'src/transformer/transformer.dart';